Directional coupler



p 6, 1960 R. E. STONE 2,951,997

DIRECTIONAL COUPLER Filed Feb. 5, 1957 IN V EN T 0R. RODNEY E. STONE ATTORNEY side of the primary waveguide.

U ited tes DIRECTIONAL COUPLER Rodney E. Stone, Pomona, "Califl, assignor to General Dynamics Corporation, San Diego, Calif., a corporation of Delaware Filed Feb. 5,1951, Ser. No. 638,279

6 Claims. (Cl. 3s3 -10 -is highly satisfactory for rectangular waveguide operating in the TE 0, 1 mode, it cannot be employed in connection with waveguides and modes wherein low field intensities are present at the adjacent sides. Ridged waveguideoperating in the dominant mode,for example, has very low field intensities at the adjacent walls of crossing waveguides. Thus, the conventional manner of directionally coupling crossing waveguides through crossed slots cannot be employed in connection with ridged waveguides. The crossing waveguide directional coupler of this invention employs directional coupling means which enables waveguide with low field intensities at adjacent sides, such as double ridge waveguide, to be directionally coupled with a large energy transfer from one waveguide to another along with high directivity of transferred energy. Conducting probes, suitably mounted in insulating holders, extend from one double ridge waveguide to the other through apertures in the adjacent walls thereof. I It is, therefore, an object of this invention to provide means 'for directionally coupling crossing double ridge waveguide.

Another object of this invention is to provide a double ridge waveguide directional coupler providing energy probe coupling through adjacent walls.

Another object of this invention is to provide a crossed double ridge waveguide directional coupler having probe couplings extending through adjacent walls.

Another object of this invention is to provide a directional coupler for crossing waveguide which provides high energy transfer and directivity in waveguide having low field intensities at adjacent, crossing walls.

Another object of this invention is to provide a double ridge waveguide directional coupler which is eflicient, compact, light, and inexpensive to manufacture.

Other objects and advantages of this invention will become apparent from study of the following description taken in connection with the accompanying drawing, wherein:

t Figure 1 illustrates a perspective view of a waveguide structure embodying this invention; and

Figure 2 illustrates an end view, partially cut away, of the directional coupler of Figure 1 taken from the left Referring now to the drawings, and particularly to Patented Sept. 6, 1960 Figure 1, there is shown a primary waveguide 11 and a secondary waveguide 12 crossing one another. Illustrated waveguides 11 and 12 are double ridge waveguides having ridges one third the overall width of the waveguide extending into the interior of each side of the waveguide approximately one third the depth thereof. Primary waveguide 11 is afiixed to secondary waveguide 12 by any suitable means, such as welding, brazing, soldering, etc. Circular apertures 13 and 14 are provided in each of the outermost walls of waveguide 11, respectively. Circular apertures 15 and 16, in line with apertures 13 and 14 respectively, illustrated in Figure 2, are provided in the outer wall of waveguide 11 which is in contact with waveguide 12. A portion of outer walls of waveguide 12 adjacent to the outer walls of waveguide 11 are cut away to receive waveguide 11, as illustrated by Figure 2.

Hollow cylindrical rod 17 (cut away), extends through apertures 13 and 15 through the interior of waveguides 11 and 12, abutting against the interior side of the far wall of waveguide 12. In a similar fashion, hollow cylindrical rod 21 extends through apertures 14 and 16 through the interior of waveguides 11 and 12, abutting against the interior side of the far wall of waveguide 12. Cylindrical rods 17 and 21 are fabricated of a suitable high frequency insulating material.

A metallic probe 22 fits snugly in the hollow interior of insulating rod 21. The length of the aperture in insulating rod 21 is such that half of metallic probe 22 extends into waveguide 12, the other half extending into waveguide 11. An insulating spacing retainer 23, preferably fabricated of the same material as hollow rod 21, retains probe 22 in coupling position. Threaded metallic cap 24, cooperating with threaded aperture 14, retains the coupling assembly comprising hollow rod 21, coupling probe 22 and spacing retainer 23 in operating position in waveguides 11 and 12. A similar threaded metal cap 25, cooperating with threaded aperture 13, retains a substantially identical coupling assembly comprising hollow rod 17 and a coupling probe and spacer, not shown, but substantially identical to coupling probe 22 and spacer 23.

As is well known in the art, a directional coupler, when coupled to a primary waveguide, responds only to a wave traveling in a particular direction in the primary waveguide, launching a wave in a particular direction in a secondary waveguide. In the directional coupler of this invention, a portion of a wave traveling from left to right in primary waveguide 11 in Figure 1 is coupled into secondary waveguide 12, traveling only from left to right therein as viewed in Figure 1. Similarly, a portion of a wave traveling from right to left in primary waveguide 11 is coupled into secondary waveguide 12, traveling from right to left as viewed in Figure l.

A probe such as probe 22, illustrated in Figure 2, is associated with both of apertures 13 and 14, substantially half of each probe extending into waveguide 11 and half into waveguide 12. The probes are placed substantially a quarter wavelength from one another, the wavelength being that measured in the waveguide. Although the directional coupler of this invention has a broad frequency response, directivity at a desired frequency may be maximized by varying the distance between the probes, as by varying the angle of intersection from the perpendicular position illustrated. Since adjacent sides of the ridged waveguides 11 and 12 are areas of low field intensity, the probes are of sufiicient length to couple the strong electric field near the center of ridge waveguide 11 to the center of ridge waveguide 12, establishing a field therein.

Each probe launches a wave in both directions in waveguidelZ. However, the waves traveling in the desired direction add in phase, while the waves traveling in the opposite direction cancel out. A resistance termination may be placed at one end of secondary waveguide 12 to attenuate any wave traveling in'the undesired direction as a result of incomplete cancellation, thereby avoiding a standing wave in waveguide 12. The amount of energy from waveguide 11 coupled into waveguide 12 may be varied by varying the lengths of the probes.

It will be seen that the present invention provides a new and improved directional coupling device which is relatively simple and inexpensive and which is adapted to provide high directivity and controlled coupling at high frequencies. This invention enables a crossed type of directional coupler to be constructed of waveguide having low field intensities at adjacentwalls, such as ridged waveguide. The coupling device disclosed herein will handle high powers over a wide band of frequencies.

Since various changes may be made in the form, construction and arrangement of the parts herein without departing from the spirit and scope of the invention, it is to be understood that all matter contained in the above description and the accompanying drawings shall be interpreted as illustrative only.

What I claim is:

l. A directional coupler comprising a primary ridge waveguide, a secondary ridge waveguide externally crossing said primary ridge waveguide, the crossing of said ridge waveguides defining a rectilinear area of intersection, first and second coupling means positioned along a diagonal of said rectilinear area of intersection, each of said coupling means including a cylindrical, conductive probe responsive only to electric fields extending from the interior of said primary ridge waveguide to the interior of said secondary ridge waveguide and an insulating holder separating said conductive probe from the walls of said primary and secondary ridge waveguides, whereby a wave traveling in one direction in said primary ridge waveguide induces a wave traveling in a predetermined direction in said secondary ridge waveguide.

2. A directional coupler including a primary waveguide and a secondary waveguide, said primary and secondary waveguides having a rectangular cross section with a pair of wide walls and a pair of narrow walls, said wide walls having a central ridge projecting into the interior of said waveguide, said primary waveguide crossing said secondary wiveguide with said wide walls adjacent thereby defining a rectilinear area of intersection, first and second coupling means positioned along a diagonal of said rectilinear area of intersection, each of said coupling means including a cylindrical, conductive probe responsive only to electric fields extending from the interior of said primary waveguide into the interior of said secondary waveguide and an insulating holder separating said conductive probe from the walls of said primary and secondary waveguides, whereby a wave traveling in one direction in said primary waveguide induces a wave traveling in a predetermined direction in said secondary waveguide.

3. A directional coupler including a primary waveguide and a secondary waveguide, said primary and secondary waveguides having a rectangular cross section with a pair of wide walls and a pair of narrow walls, said wide walls having a central ridge projecting into the interior of said waveguide, said primary Waveguide crossing said secondary waveguide with said wide walls adjacent, thereby defining a rectilinear area of intersection, first and second coupling means positioned along a diagonal of said rectilinear area of intersection, each of said coupling means including a cylindrical metal probe respoonsive only to electric fields extending from the interior of said primary waveguide into the interior of said secondary waveguide, a hollow cylindrical holder of insulating material enclosing said probe and separating said probe from the walls of said primary and secondary waveguides, whereby a wave traveling in one direction in said primary waveguide in:

duces a wave traveling in a predetermined direction in said secondary waveguide.

4. A directional coupler including a primary waveguide and a secondary waveguide, said primary and secondary waveguides having a rectangular cross section with a pair of wide walls and a pair of narrow walls, said wide walls having a central ridge projecting into the interior of said waveguide, said primary waveguide crossing said secondary waveguide with said wide walls adjacent, thereby defining a rectilinear area of intersection, first and second coupling means positioned along a diagonal of said rectilinear area of intersection, each of said coupling means including a cylindrical metal probe responsive only to electric fields extending from the interior of said primary waveguide into the interior of said secondary waveguide through apertures in said adjacent wide walls and a hollow cylindrical holder of insulating material enclosing said probe and separating said conductive probe from the walls of said primary and secondary waveguides, whereby a wave traveling in onedirection in said primary waveguide induces a wave traveling in a predetermined direction in said secondary waveguide.

5. A directional coupler including a primary waveguide and a secondary waveguide, said primary and secondary waveguides having a rectangular cross section with a pair of wide walls and a pair of narrow walls, said wide Walls having a central ridge projecting into the interior of said waveguide, said primary waveguide crossing said secondary waveguide perpendicularly with said wide walls adjacent, thereby defining a square area of intersection, first and second coupling means positioned along a diagonal of said square area of intersection adjacent -to said central ridge, each of said coupling means including a cylindrical metal probe responsive only to electric fields extending from the interior of said primary waveguide into the interior of said secondary waveguide through apertures in said adjacent wide wall, a hollow cylindrical holder of insulating material enclos-ing said probe and separating said conductive probe from the walls of said primary and secondary waevguides, whereby a wave traveling in one direction in said primary waveguide induces a wave traveling in a predetermined direction in said secondary waveguide.

6. A directional coupler including a primary waveguide and a secondary waveguide, said primary and secondary waveguides having a rectangular cross-section with an opposing pair of wide walls and an opposing pair of narrow walls, each of said wide walls having a central ridge projecting into the interior of. said waveguides, said primary waveguide crossing said secondary waveguide with said wide walls adjacent, thereby defining a rectilinear area of intersection, first and second coupling means positioned a quarter wavelength apart along a diagonal of said rectilinear area of intersection adjacent to said central ridge, each of said coupling means in cluding a cylindrical metal probe responsive only to electric fields having equal lengths extending into the interior of said primary waveguide and into the interior of said secondary waveguide through apertures in said adjacent wide walls, a hollow cylindrical holder of insulating material closed at one end enclosing said probe and separating said probe from the adjacent inner wide walls of said primary and secondary waveguides and the outer wide wall of said secondary waveguide, a cylindrical spacer of insulating material enclosed in said holder adjacent the end of said cylindrical metal probe facing the outer wide wall of said primary waveguide, and a metallic cap in the outer wide Wall of said primary waveguide adjacent said cylindrical holder retaining said holder, spacer, and probe in operative relationship with said primary and secondary waveguides, whereby a wave traveling in one direction in said primary waveguide induces a wave traveling in a predetermined direction in said secondary waveguide.

(References on following page) 5 6 References Cited in the file of this patent FOREIGN PATENTS Great Britain Feb- 4, 2,580,678 Hansen et a1. Jan. 1, 1952 OTHER REFERENCES 2,580,679 Hansen Jan. 1, 1952 5 Ragan: Microwave Transmission Circuits, published 2,602,859 Moreno July 8, 1952 by McGraw-Hill Book Co., Inc., N.Y., in 1948, page 2,760,057 Johannesen Aug. 21, 1956 358. 

